The objective of this application is to develop an accurate high-throughput genotoxicity screening system with high specificity and accuracy using our established and well-validated toxicogenomic biomarker in cultured human cells. Genotoxicity represented by chromosome damage and mutations in DNA is considered to be the hallmark of carcinogenic risk. The standard genotoxicity assays, especially in the case of in vitro chromosome aberration assays, have a high false positive rate which results in costly and time consuming follow up assays that increase the cost of drug development and chemical safety assessment. Hence, gaining insight into genotoxic mechanisms and distinguishing those false positive genotoxicity findings caused by nongenotoxic mechanisms is of great value, so a simple, reliable technology proposed here would be sought after by pharmaceutical and chemical companies. Our biomarker, TGx-28.65, is capable of recognizing incorrectly identified compounds. The specificity of genotoxicity prediction by TGx-28.65, the intra- and inter- laboratory reproducibility, and the reproducibility on different technical platforms have been carefully validated by us and by a second laboratory in follow-up studies. Our TGx-28.65 biomarker recently was incorporated into the ?1500 Genes? panel for the Tox21 Phase III high throughput transcriptomics project. In the Phase I feasibility project we propose to develop a commercially viable and efficient high-throughput genotoxicity screening system using TGx-28.65, which has shown remarkable specificity and robustness for genotoxicity prediction. Our technical approach will employ direct digital counting technology to achieve high levels of precision, linearity, and reproducibility in measuring the expression levels of 65 genes in TGx-28.65 simultaneously. The proposed approach will provide significant benefits in comparison to the current genotoxicity battery and is poised to be commercially successful.